Roberts, 19, scored 92.1 points on the lead wall, taking his overall score to 155.2 points after placing third in the boulder round.
Anraku, the favourite to clinch the title in Paris, had been in front after the boulder section but fell on his final lead climb and had to settle for silver, with 145.4 points.
Austria's Jakob Schubert won bronze with 139.6 points.
"I've got no words. I'm just riding on adrenaline right now, but I feel incredible," said Roberts.
"I already knew I had won the silver medal, so I was really happy anyway just watching him (Anraku).
"Then (when Anraku fell) to realise that I had just become Olympic champion, I was just 'Wow, no words'."
Spain's Alberto Gines Lopez, the first Olympic champion in the discipline at the Tokyo Games, finished seventh on front of a crowd of more than 6,000 at the Le Bourget climbing venue.
UK teen Toby Roberts clinches Olympic climbing gold
FE Team | Published: August 09, 2024 22:48:49
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